[Paper Review] Long Range Plan: Dense matter theory for heavy-ion collisions and neutron stars

Alessandro Lovato, Travis Dore+62 more|arXiv (Cornell University)|Nov 4, 2022

Gamma-ray bursts and supernovaePhysics and Astronomy18 citations

TL;DR

This Long Range Plan outlines a unified theoretical framework for studying dense baryonic matter in heavy-ion collisions and neutron stars, integrating nuclear physics, astrophysics, and quantum computing. It proposes leveraging quantum simulations and entanglement measures to probe non-equilibrium QCD dynamics, thermalization, and phase transitions—particularly via noisy intermediate-scale quantum computers for near-term insights into strongly correlated matter.

ABSTRACT

Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theory of dense baryonic matter that connects low- and high-energy nuclear physics, astrophysics, gravitational waves physics, and data science

Motivation & Objective

• To advance the theoretical understanding of dense baryonic matter in extreme conditions, such as those in neutron stars and heavy-ion collisions.
• To bridge low-energy nuclear physics, high-energy QCD, astrophysics, and gravitational wave observations through a unified theoretical framework.
• To identify near-term quantum computing applications for simulating non-equilibrium QCD phenomena, including thermalization and entanglement dynamics.
• To explore the role of quantum entanglement and eigenstate thermalization in explaining rapid equilibration in strongly interacting systems.
• To guide the development of effective field theories and quantum algorithms that can access non-perturbative observables like parton distribution functions and transport coefficients.

Proposed method

• Utilize effective field theories to factorize short-distance perturbative amplitudes from long-distance non-perturbative matrix elements.
• Employ quantum computers to compute non-perturbative matrix elements—such as parton distribution functions and hadronic tensors—more efficiently than full quantum simulations.
• Apply quantum algorithms to prepare initial hadronic and thermal states on quantum hardware, enabling real-time evolution studies.
• Use entanglement spectrum analysis and level spacing distributions to diagnose thermalization and phase transitions in quantum many-body systems.
• Implement quench protocols on noisy intermediate-scale quantum computers to probe dynamical quantum phase transitions and non-equilibrium dynamics.
• Explore the eigenstate thermalization hypothesis (ETH) as a mechanism for explaining fast thermalization in isolated quantum systems.

Experimental results

Research questions

• RQ1 How can quantum computing be used to compute non-perturbative matrix elements in QCD with lower resource cost than full simulations?
• RQ2 What role does quantum entanglement play in the rapid thermalization of strongly interacting matter, and how can it be probed experimentally or computationally?
• RQ3 Can noisy intermediate-scale quantum computers reliably simulate key transport coefficients and parton distribution functions relevant to relativistic hydrodynamics?
• RQ4 How do entanglement spectra and spectral gaps signal phase transitions and equilibration in non-equilibrium QCD systems?
• RQ5 What near-term quantum algorithms and protocols can provide qualitative insight into the dynamics of gauge theories out of equilibrium?

Key findings

• Quantum computing offers a viable path to compute non-perturbative observables like parton distribution functions and transport coefficients at reduced computational cost compared to full lattice QCD simulations.
• Entanglement spectrum analysis can reveal signatures of thermalization and phase transitions, with level spacing distributions indicating whether a system thermalizes.
• Noisy intermediate-scale quantum computers can potentially simulate quench dynamics and dynamical quantum phase transitions in gauge theories, even with current hardware limitations.
• The eigenstate thermalization hypothesis provides a theoretical foundation for understanding rapid equilibration in isolated quantum systems, which can be tested via entanglement measures.
• Thermal states at arbitrary densities can be efficiently prepared on quantum computers, enabling exploration of the QCD phase diagram in principle.
• Quantum simulations of real-time evolution are essential for studying the approach to equilibrium and the role of entanglement in non-equilibrium QCD dynamics.